This invention relates to optical attenuators, in particular to variable optical attenuators with mechanical adjustment.
Variable optical attenuators are used to attenuate light beams in optical systems such as fiber optic communication systems. Controllably attenuating a light beam can be achieved by various methods, such as by passing the beam through a variable-attenuation (e.g. wedge-shaped) filter, radially bending a fiber loop to vary the optical loss within the loop, thermally changing the refractive index of cladding material, and partially blocking the beam by inserting a beam block into the light beam path.
Beam-blocking attenuators can act in a wavelength- and polarization-independent manner, and can have high reliability and repeatability. In addition, beam-blocking attenuators allow wide attenuation ranges, and can be relatively easy to manufacture. At the same time, beam-blocking attenuators can be relatively bulky. Moreover, achieving high resolutions with beam-blocking attenuators may require very fine (micron-level) mechanical control or tolerances.
In U.S. Pat. No. 6,167,185, Smiley et al. disclose an optical attenuator for attenuating a light beam while preserving the polarization of the light beam. The optical attenuator includes a beam attenuator for attenuating the light beam when disposed within the path of the light beam. The beam attenuator has a cross-section along a plane perpendicular to the direction of propagation of the light beam in the shape of a wedge. Smiley et al. teach that the disclosed attenuator preserves the polarization composition of the light beam over a large attenuation range. At the same time, the resolution of the attenuator described by Smiley et al. can be limited for a given beam attenuator size and precision of motion.
The present invention provides a variable optical attenuator for attenuating a longitudinal light beam, comprising a generally transverse beam attenuator for attenuating the light beam, the beam attenuator having a proximal end, a distal tip, and a concave curved light-blocking surface extending between the proximal end and the distal tip, the blocking surface narrowing from the proximal region to the distal tip. A control device is coupled to the beam attenuator, for controlling a motion of the beam attenuator so as to vary an attenuation of the light beam caused by the beam attenuator. The optical attenuator has a variable resolution depending on an extent of the blocking surface blocking the light beam. The inwardly-curved boundary of the light-blocking surface allows improved attenuation resolutions relative to a conical light-blocking surface of the same overall size. The light beam can be a single- or multi-mode laser beam.